Join TSR now and get all your revision questions answeredSign up now

Probability "With Replacement" Watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    A fireworks warehouse stores 500 bottle rockets, of which 40 are assumed to be duds (meaning that they wouldn't fire if lighted).

    If 10 bottle rockets are randomly selected with replacement, then what is the probability that 5 of those selected are duds (to four decimal places)?

    (I've been told that the answer is 0.0005 but I'm not sure how to get this answer, someone please help!!)
    Offline

    2
    ReputationRep:
    (Original post by SP1234321)
    A fireworks warehouse stores 500 bottle rockets, of which 40 are assumed to be duds (meaning that they wouldn't fire if lighted).

    If 10 bottle rockets are randomly selected with replacement, then what is the probability that 5 of those selected are duds (to four decimal places)?

    (I've been told that the answer is 0.0005 but I'm not sure how to get this answer, someone please help!!)
    It's hard because you can't do it directly, since you don't know which 5 are to be duds. What you need to spot is that if X is the number of bottle rockets that are duds out of the 10 selected, then X has a binomial distribution (with parameters that you should determine). So can you now find the answer P(X=5)?
    Online

    3
    ReputationRep:
    "With replacement" just means that once a rocket is taken from the population and recorded, it is then replaced by an identical rocket (or it's put back if you prefer). So the total population remains at 500 instead of decreasing.

    Does that help?
 
 
 
Write a reply… Reply
Submit reply
Updated: June 19, 2017
Poll
Still A Remainer Or A Brexiteer?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.